This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | -2 |
| 2 | 6 |
| 3 | -18 |
| 4 | 52 |
| 5 | -152 |
| 6 | 444 |
| 7 | -1296 |
| 8 | 3784 |
| 9 | -11048 |
| 10 | 32256 |
| 11 | -94176 |
| 12 | 274960 |
| 13 | -802784 |
| 14 | 2343840 |
| 15 | -6843168 |
| 16 | 19979584 |
| 17 | -58333184 |
| 18 | 170311872 |
| 19 | -497249280 |
| 20 | 1451788672 |
| 21 | -4238699648 |
| 22 | 12375475200 |
| 23 | -36131927040 |
| 24 | 105492203776 |
| 25 | -307999212032 |
| 26 | 899246685696 |
| 27 | -2625476203008 |
| 28 | 7665444201472 |